1. Field of the Invention
The invention relates to an acoustic target simulator for use primarily with sonar-equipped torpedoes.
In active sonar systems, sometimes called echo repeater systems, pulses are sent out from a submerged transmitter. If the pulses strike a target, they are reflected back in the direction of the transmitter where a submerged receiver picks up the reflected signal. The repetition rate of the pulses generally varies with the distance between the target and the transmitter and may serve to give information about the distance between them. A passive sonar system normally consists only of a submerged receiver which listens for noises generated by a possible target. Passive sonar systems have the advantage of being undetectable themselves and are most commonly used on submarines.
Active and passive sonar systems are mounted on ships as well as torpedoes. The primary purpose of a ship mounted sonar system is to locate submerged targets and therefore their active sonars utilize low frequency wide-beam signals. The primary purpose of the torpedo sonars on the other hand is to guide the torpedo to a target. Consequently, the signal emitted by active torpedo sonars is a high frequency narrow beam signal.
2. Description of the Prior Art
Various means are known in the prior art to simulate targets for active and passive sonars. These devices have a single receiver and a single transmitter and sometimes include a noise generator. They are operable either to generate noise or upon receipt of a sonar signal to amplify the signal and retransmit it. The retransmitted signal is similar to the echo produced by a submerged submarine or the hull of a surface vessel when a sonar signal is bounced off of it. These devices may provide a good acoustic pattern in one direction from the transmitter but have a hole or shadow in the other direction due to the body of the simulator.
As the sonar signal transmitted from an active ship-mounted sonar is sent out in a wide beam, the shadow produced by the vehicle body of the target is not as critical a factor as with the sonar-equipped torpedo. The narrow beam of the torpedo signal renders those devices which only provide a single transmitter and receiver unsuitable for use with active sonar-equipped torpedoes because the holes produced in the acoustic pattern may cause the torpedo to miss the simulator.
The standard evasive actions which submarines take against sonar-equipped torpedoes are silence and the deployment of expendable decoys. Surface vessels sometimes avoid such torpedoes by deploying explosive depth charges. The target simulators of the prior art are limited in that they are incapable of simulating such evasive actions.